This invention relates to processes and apparatus for recovering sulfur. In particular, it relates to cooling and condensing sulfur and water from gaseous streams, such as, from the gas of a Claus process.
The Claus process is widely used by industry for production of elemental sulfur. The process is designed to carry out the Claus reaction: EQU 2H.sub.2 S+SO.sub.2 .revreaction.2H.sub.2 O+3S
A catalyst may be used for the reaction. The reactio is favored by the condensation and removal of water.
It is not possible to obtain complete conversion to sulfur by this reaction because the ratio of H.sub.2 O/H.sub.2 S in the gas increases with increasing conversion and because this ratio has a limit determined by thermochemical equilibrium (and by the concentrations of SO.sub.2 and sulfur vapor in the gas). In recent years these plants have been required by governmental agencies to obtain higher conversion of the H.sub.2 S and SO.sub.2 to product sulfur, in order to decrease the air pollution resulting from discharge of the sulfur plant tail gas incinerator effluent into the atmosphere. Several methods have been developed to accomplish this, and these are generally referred to as tail gas cleanup methods. However these methods are complex, they have high investment and operating costs, and they require considerable energy to operate.
A preferred alternate method for converting additional H.sub.2 S and SO.sub.2 to sulfur would be to reduce the water concentration before each catalytic reaction stage of the Claus process, or at least before the final stage. This method has not been used because there has not been a practical method available for condensing and removing the water.
A method that could be used for cooling the gas to effect the condensation of water is a quench system such as that disclosed in U.S. Pat. No. 3,681,024 (Hujsak and Palm). However, such quench system is complicated and therefore expensive to manufacture and to operate.
The use of a simple water quench system suffers from yet another problem. Such system would result in the condensation of sulfur vapor from the gas stream in colloidal or other undesirable form. The resulting sulfur would have to be remelted or otherwise converted into a useful form.
There is therefore a long felt and still unsatisfied need for an inexpensive process that would condense water from gas streams in a Claus process with low energy consumption and without condensing sulfur in colloidal or other undesirable form. The present invention achieves the above-stated goal with a process which utilizes simple, reliable and inexpensive equipment that can be manufactured from commercially available parts.